If you remove the stiffer spring , with just the lighter spring , you can set it at 18 initial and get about 18 mechanical advance by around 1500rpm.
The light spring is done by the time you cross the intersection. The stiff slotted spring will lengthen the curve
Those things, some, didnt full adavance till 4800 rpm. You leave that spring and wels the inside, you take up the slot . It starts under tension.
I dont bother with any of that on a stock distributor anymore, I run an msd . I ground down and egg shaped nut to get the curve I find my motor likes. Typically the same or close to the last motor...because it's the same car. I use a blue spring iirr. If I were messing with stock dizzys I'd use a mr.gasket light spring where the heavy is and call it a day. They came up with one light or 2 because the timing bounces with a mere 200 rpm drastically with only one mr.gasket light or stock light and nothing else. You can do it how you like. I don't think we are that far apart.
